Clone and Iterative Adapter Methods in Rust: The thin line between Duplication, Efficiency and Transformation

As a rust developer, it is a dilemma you would always have to deal with: the choice between clone and iterative methods. In this guide, we will be exploring what these methods are, the fundamental differences between them, how they can be useful in manipulating data and which is appropriate for particular situations.

The Clone method

The clone method (clone()) is used to implement or "create" deep copies of an object or data. It operates by duplicating the entire object structure and reallocating new memory for the copied instance of that object.

Note: When we refer to the term reallocating, this is most likely a reference to heap-allocated data i.e. dynamic allocated memory for complex data collections(e.g., String, Vec, Box). When using clone() with stack-only types (e.g., char, i32), we do not reallocate memory as it simply copies the data directly on the stack.

In simpler terms, the clone method generates two independent instances of the same data

fn main() {
    let args: Vec<String> = env::args().collect();

    let config = parse_config(&args);

    println!("Searching for {}", config.query);
    println!("In file {}", config.file_path);

    let contents = fs::read_to_string(config.file_path)
        .expect("Should have been able to read the file");

    // --snip--
}

struct Config {
    query: String,
    file_path: String,
}

fn parse_config(args: &[String]) -> Config {
    let query = args[1].clone();
    let file_path = args[2].clone();

    Config { query, file_path }
}

In the code snippet above, we make a full copy of the data for the Config instance to own by cloning the values received through args, which takes more time and memory than storing a reference to the string data.

Iterator Adapter Method
In comparison to the clone(), iterator adapter methods are used to transform and process elements of an iterator. They are usually referred to as lazy in rust, and this is because iterator methods will not effect any process until the methods that consume the iterator is called. These consumption methods also known as consuming adapters, i.e methods that use up the (e.g., sum(), next()….) will be discussed when we talk about iterator methods in details.
Iterator Adapters(different from consuming adapters) do not immediately produce new data, hence the term "lazy'. Instead they return a new iterator that processes these data as they are needed on demand.

Differences between Clone Methods and Iterator Adapter Methods

Memory Allocation:

Clone Method:

Clone methods will create a new copy of the data. This can lead to additional memory allocation and therefore can be computationally expensive, especially for large or complex data structures, as it requires duplicating the entire object.

let v = vec![1, 2, 3];
let v2 = v.clone(); // Creates a deep copy of the entire vector
println!("{:?}, {:?}", v, v2);

Iterator Adapter Method:

Iterators generally operate in a lazy fashion, so they will not allocate memory immediately. They transform or process data as you iterate over it and this can make them more memory-efficient than clone methods. Also, allocation with iterators occurs only when you consume the iterator (e.g., using .collect() to gather results into a new collection).

let v = vec![1, 2, 3];
let iter = v.iter().map(|x| x * 2); // Creates a lazy iterator, no memory allocation yet
let v2: Vec<_> = iter.collect();    // Consumes the iterator and collects the results into a new vector
println!("{:?}, {:?}", v, v2);

Data Ownership and Borrowing:

Clone Method:

When an object is cloned, a new owned instance of that object data is initiated. Therefore, both the original and the cloned object can co-exist independently with no ownership conflict between them.

Iterator Adapter Method:

Iterators can either borrow data from the original collection or take ownership of the elements. Many iterator methods do not require ownership (for example, the iter() returns an iterator that borrows the data).

This borrowing mechanism is very useful when you need multiple copies of data that can be modified separately therefore making them more flexible when you want to process elements without transferring ownership or duplicating data.

So now you know the difference between them, which should you use?

Well it is going to depend on your specific use case but as a general rule of thumb, You use clone methods when you:

• wish to create a deep copy of an object, instantly allocating new memory for the instance.
• want an independent, identical copy of an object that can be modified or passed elsewhere without affecting the original object.

You use Iterator Adapter Methods when you:

• want to transform, filter, or aggregate data from a collection or stream in a lazy, efficient way.
• Do not need immediate memory allocation

But here is something you should keep in mind, aside from the specific use cases considered above, clone methods are generally inefficient because of its runtime cost. The idea of deeply copy data can impact performance especially if it is a large and complex data.
Iterative methods on the other hand are more efficient since you do not need to create any intermediate collections unless explicitly required by the program.
Iterative methods are also more performant efficient than loops. By combining them with closures, which we shall talk about when we discuss Iterative adapters in detail, we can harness Rust’s capability to clearly express high-level ideas at low-level performance.